The specific aims of this research are to learn how blood and cerebrospinal fluid (CSF) concentrations of the anterior pituitary hormones, adrenocorticotrophin (ACTH), beta-endorphin (Beta-E), and prolactin (PRL), are related and to what extent CSF concentrations of these peptides reflect brain peptidergic activity. Recent studies suggest that measurements of peptides in CSF might be useful for the diagnosis and understanding of neurological and psychiatric illnesses. However, it is not completely understood what influences peptide concentrations in CSF and to what degree such concentrations are affected by the brain. We will simultaneously and frequently sample blood and CSF from rhesus monkeys, and measure peptide concentrations with radioimmunoassays. To study the dynamics of the relationship between blood and CSF peptide concentrations in normal monkeys, we will use various pharmacological and nonpharmacological challenges to alter peripheral peptide concentrations. We will perform similar studies in hypophysectomized monkeys to directly observe how the brain contributes to CSF peptide concentration, independent of the major peripheral source of these hormones.